Method and apparatus for predictive scheduling in a bi-directional communication system

ABSTRACT

Method and apparatus for predictive scheduling in a bi-directional communication system are disclosed. In a communication system ( 100 ), a control unit ( 218 ) has knowledge that a subscriber station ( 106 ) will have data to be transmitted at an ascertainable time in the future. The control unit in the communication system utilizes the knowledge to schedule the data transmission without the need for the subscriber station to transmit to request schedule for the transmission.

BACKGROUND

1. Field

The present invention relates generally to communication systems, andmore specifically to a method and an apparatus for predictive schedulingin a bi-directional communication system.

2. Background

Communication systems have been developed to allow transmission ofinformation signals from an origination station to a physically distinctdestination station. In transmitting information signal from theorigination station over a communication channel, the information signalis first converted into a form suitable for efficient transmission overthe communication channel. Conversion, or modulation, of the informationsignal involves varying a parameter of a carrier wave in accordance withthe information signal in such a way that the spectrum of the resultingmodulated carrier is confined within the communication channelbandwidth. At the destination station the original information signal isreplicated from the modulated carrier wave received over thecommunication channel. Such a replication is generally achieved by usingan inverse of the modulation process employed by the originationstation.

Modulation also facilitates multiple-access, i.e., simultaneoustransmission and/or reception, of several signals over a commoncommunication channel. Multiple-access communication systems ofteninclude a plurality of subscriber subscriber units requiringintermittent service of relatively short duration rather than continuousaccess to the common communication channel. Several multiple-accesstechniques are known in the art, such as time division multiple-access(TDMA), frequency division multiple-access (FDMA), and amplitudemodulation multiple-access (AM). Another type of a multiple-accesstechnique is a code division multiple-access (CDMA) spread spectrumsystem that conforms to the “TIA/EIA/IS-95 Mobile Station-Base StationCompatibility Standard for Dual-Mode Wide-Band Spread Spectrum CellularSystem,” hereinafter referred to as the IS-95 standard. The use of CDMAtechniques in a multiple-access communication system is disclosed inU.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESSCOMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S.Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMSIN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee ofthe present invention.

A multiple-access communication system may be a wireless or wire-lineand may carry voice and/or data. An example of a communication systemcarrying both voice and data is a system in accordance with the IS-95standard, which specifies transmitting voice and data over thecommunication channel. A method for transmitting data in code channelframes of fixed size is described in detail in U.S. Pat. No. 5,504,773,entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FORTRANSMISSION”, assigned to the assignee of the present invention. Inaccordance with the IS-95 standard, the data or voice is partitionedinto code channel frames that are 20 milliseconds wide with data ratesas high as 14.4 Kbps. Additional examples of a communication systemscarrying both voice and data comprise communication systems conformingto the “3rd Generation Partnership Project” (3GPP), embodied in a set ofdocuments including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 PhysicalLayer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000standard).

An example of a data only communication system is a high data rate (HDR)communication system that conforms to the TIA/EIA/IS-856 industrystandard, hereinafter referred to as the IS-856 standard. The HDR systemis based on a communication system disclosed in co-pending applicationSer. No. 08/963,386, entitled “METHOD AND APPARATUS FOR HIGH RATE PACKETDATA TRANSMISSION,” filed Nov. 3, 1997, assigned to the assignee of thepresent invention. The HDR communication system defines a set of datarates, ranging from 38.4 kbps to 2.4 Mbps, at which an access point (AP)may send data to a subscriber station (access terminal, AT). Because theAP is analogous to a base station, the terminology with respect to cellsand sectors is the same as with respect to voice systems.

In a multiple-access communication system, communications between usersare conducted through one or more base stations. A first user on onesubscriber station communicates to a second user on a second subscriberstation by transmitting data on a reverse link to a base station. Thebase station receives the data and can route the data to another basestation. The data is transmitted on a forward link of the same basestation, or the other base station, to the second subscriber station.The forward link refers to transmission from a base station to asubscriber station and the reverse link refers to transmission from asubscriber station to a base station. Likewise, the communication can beconducted between a first user on one mobile subscriber station and asecond user on a landline station. A base station receives the data fromthe user on a reverse link, and routes the data through a publicswitched telephone network (PSTN) to the second user. In manycommunication systems, e.g., IS-95, W-CDMA, IS-2000, the forward linkand the reverse link are allocated separate frequencies.

The design of a multiple-access communication system causes eachtransmitting subscriber station to act as an interference to othersubscriber stations in the network. Therefore, the reverse link capacityis limited by the total interference which a subscriber stationexperiences from other subscriber stations. The amount of interferenceis affected by the mode of operation of the communication system—speech,data, or speech and data.

The amount of speech activity at any given moment is non-deterministic.In addition, there is typically no correlation in the level of speechactivities among users. Therefore, the total power received at the basestation from all transmitting subscriber stations varies over time andcan be approximated as a Gaussian distribution. During periods of activespeech, the subscriber station transmits at higher power and causes moreinterference to other subscriber stations. More interference increasesthe probability of frame errors in the voice data received by the basestation. Therefore, the capacity, i.e., the number of users able to haveaccess to the communication system is limited so that only a smallportion of the transmitted frames is lost through excessiveinterference. In contrast, data communication is typically characterizedby long period of inactivity, or low activity, punctuated by high burstsof data traffic that drastically decrease the communication systemcapacity.

Because of the variations in the level of voice activities, and thetransmission of data traffic concurrently with the voice traffic, thedemand for the reverse link continuously changes over time. To avoiddegradation in the quality of the voice communication, the utilizationof the reverse link should be dynamically adjusted to match theavailable reverse link capacity of the base station.

One method of minimizing the interference and maximizing the reverselink capacity is to control the transmit power of each subscriberstation. For example, the communication system in accordance with theIS-95 standard utilizes two control loops. The first power control loopadjusts the transmit power of the subscriber station such that thesignal quality, as measured by theenergy-per-bit-to-noise-plus-interference ratio, E_(b)/(N_(o)+I_(o)), ofthe signal received at the cell is maintained at a constant level. Thislevel is referred to as the E_(b)/(N_(o)+I_(o)) set point. The secondpower control loop adjusts the set point such that the desired level ofperformance, as measured by the frame-error-rate (FER), is maintained.The power control mechanism for the reverse link in IS-95 is disclosedin detail in U.S. Pat. No. 5,056,109, entitled “METHOD AND APPARATUS FORCONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONESYSTEM”, assigned to the assignee of the present invention.

In accordance with another method, each subscriber station transmits ata different bit rate depending on the level of speech activity in theconversation of a user on the subscriber station. A variable rate speechvocoder provides speech data at full rate when the user is activelyspeaking and at low rate during periods of silence, e.g., pauses. Thevariable rate vocoder is described in detail in U.S. Pat. No. 5,414,796,entitled “VARIABLE RATE VOCODER,” assigned to the assignee of thepresent invention.

In yet another method, differences between voice services and dataservices are utilized. A significant difference between voice servicesand data services is the fact that the former imposes stringent andfixed delay requirements. Typically, the overall one-way delay of speechframes must be less than 100 ms. In contrast, the data delay can becomea variable parameter used to optimize the efficiency of the datacommunication system. Consequently, the reverse link can be continuouslymonitored and the data transmission dynamically scheduled so that thereverse link capacity is not exceeded. Several scheduling methods areknown in the art. Examples of scheduling methods are disclosed in detailin U.S. Pat. No. 5,914,950, entitled “METHOD AND APPARATUS FOR REVERSELINK RATE SCHEDULING”, and in U.S. Pat. No. 5,923,650 entitled “METHODAND APPARATUS FOR REVERSE LINK RATE SCHEDULING”, both assigned to theassignee of the present invention.

Because scheduling method has a profound effect on the performance of acommunication system, there is a need in the art for improvingscheduling methods and, consequently, utilization of the reverse link.

SUMMARY

Embodiments disclosed herein address the above-stated needs by takingadvantage of knowledge at a scheduler on a communication system that asubscriber station will have data to be transmitted to a base station atan ascertainable time in the future.

In one aspect of the invention, a scheduling of transmissions on a linkin a communication system comprises transmitting data on a first link inthe communication system; and transmitting scheduling information on thefirst link in the communication system. In one embodiment, the data andthe scheduling information are transmitted together.

In another aspect of the invention, a scheduling of transmissions on alink in a communication system comprises transmitting data on a firstlink in the communication system; and scheduling transmission on thelink in the communication system in accordance with the reception of thetransmitted data. In one embodiment, the link capacity for a basestation expecting the scheduled transmission on the link in thecommunication system in accordance with the reception of saidtransmitted data is ascertained, and a change to at least one parameterof pre-scheduled information when the ascertained reverse link capacitydoes not support said scheduled transmission is transmitted on the firstlink in the communication system. In another embodiment, the change toat least one parameter of pre-scheduled information is transmittedtogether with the transmitted data.

In yet another aspect, the scheduling of transmissions on a link in acommunication system comprises ascertaining the link capacity at a basestation expecting the pre-scheduled transmission of data on the link;and proceeding in accordance with the ascertained link capacity. In oneembodiment, transmitting scheduling information on the first link isabstained from when the ascertained reverse link capacity supports thepre-scheduled transmission of data. In another embodiment, confirmationfor the pre-scheduled transmission of data on the first link istransmitted when said ascertained reverse link capacity supports thepre-scheduled transmission of data. When said ascertained reverse linkcapacity does not support the pre-scheduled transmission of data,re-scheduling information is transmitted on the first link.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 illustrates a conceptual diagram of a communication system capableof performing scheduling in accordance with embodiments of the presentinvention;

FIG. 2 represents a block diagram of a basic architecture of thecommunication system of FIG. 1;

FIG. 3. illustrates a conceptual block diagram of a channel scheduler;and

FIG. 4 illustrates a flow diagram of a reverse link rate schedulingmethod.

DETAILED DESCRIPTION

The word “exemplary” is used exclusively herein to mean “serving as anexample, instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

The term packet is used exclusively herein to mean a group of bits,including data (payload) and control elements, arranged into a specificformat. The control elements comprise, e.g., a preamble, a qualitymetric, or other metrics known to one skilled in the art. Quality metriccomprises, e.g., a cyclical redundancy check (CRC), a parity bit, orother metrics known to one skilled in the art.

The term base station, referred to herein as an AP in the case of an HDRcommunication system, is used exclusively herein to mean the hardwarewith which subscriber stations communicate. “Cell” refers to thehardware or a geographic coverage area, depending on the context inwhich the term is used. A sector is a partition of a cell. Because asector has the attributes of a cell, the teachings described in terms ofcells are readily extended to sectors.

The term subscriber station, referred to herein as an AT in the case ofan HDR communication system, is used exclusively herein to mean thehardware with which an access network communicates. A subscriber stationmay be mobile or stationary. A subscriber station may be any data devicethat communicates through a wireless channel or through a wired channel,for example using fiber optic or coaxial cables. A subscriber stationmay further be any of a number of types of devices including but notlimited to PC card, compact flash, external or internal modem, orwireless or wireline phone. A subscriber station that is in the processof establishing an active traffic channel connection with a base stationis said to be in a connection setup state. A subscriber station that hasestablished an active traffic channel connection with a base station iscalled an active subscriber station, and is said to be in a trafficstate.

The term communication channel/link is used exclusively herein to mean asingle route over which a signal is transmitted described in terms ofmodulation characteristics and coding, or a single route within theprotocol layers of either the base station or the subscriber station.

The term reverse channel/link is used exclusively herein to mean acommunication channel/link through which a subscriber station sendssignals to a base station.

The term forward channel/link is used exclusively herein to mean acommunication channel/link through which a base station sends signals toa subscriber station.

The term code channel frame is used exclusively herein to mean a groupof bits arranged into a specific format within one frame time period.

The term soft hand-off is used exclusively herein to mean acommunication between a subscriber station and two or more sectors,wherein each sector belongs to a different cell. In the context of IS-95standard, the reverse link communication is received by both sectors,and the forward link communication is simultaneously carried on the twoor more sectors' forward links.

The term softer hand-off is used exclusively herein to mean acommunication between a subscriber station and two or more sectors,wherein each sector belongs to the same cell. In the context of theIS-95 standard, the reverse link communication is received by bothsectors, and the forward link communication is simultaneously carried onone of the two or more sectors' forward links.

Description

FIG. 1. illustrates an exemplary communication system 100 capable ofperforming scheduling in accordance with embodiments of the presentinvention. The communication system is composed of multiple cells 102a-102 g, each cell 102 being serviced by a corresponding base station104. Within the CDMA network, various subscriber stations 106 aredispersed throughout the coverage area of the communication system 100.The subscriber stations 106 communicate with the base stations 106 bytransmitting signals to the base stations 104 on a reverse link, andreceiving signals from the base stations 104 on a forward link. Forexample, subscriber stations 106 a and 106 b communicate exclusivelywith base station 104 c, subscriber stations 106 d and 106 e communicateexclusively with base station 104 d, but subscriber station 106 c, whichis located near a cell boundary is in handoff with base stations 104 cand 104 d. In one embodiment, the communication system 100 is a CDMAcommunication system, although the present invention is applicable toall wireless communication formats. In a CDMA communication system,subscriber station 106 c, which is located near a cell boundary, is in asoft handoff with base stations 104 c and 104 d. The use of soft handoffin a CDMA system is described in detail in the aforementioned U.S. Pat.No. 5,267,261. The base stations 106 are connected over a correspondingbackhaul 108 to a controller 110. The controller 110 interfaces with apublic switched telephone network (PSTN) 112 and a data networkinterface (DNI) 114.

FIG. 2 represents a block diagram of a basic architecture of thecommunication system 100 in more detail in accordance with oneembodiment. For simplicity, only one base station 104 and one subscriberstation 106 are illustrated in FIG. 2. Initially, a subscriber station106, e.g. 106 a, establishes a communication link with the base station104 c using a predetermined access procedure.

The voice call access procedure at the subscriber station 106 starts bythe subscriber station 106 a transmitting a request message to basestation 104 c on the reverse link 202. The base station 104 c receivesthe message at the antenna 206 and provides the message to aradio-frequency (RF) unit 208. The RF unit 208 filters, amplifies,downconverts, and quantizes the reverse link signal and provides adigitized baseband signal to one of channel elements 210, e.g., 210 a.(For simplicity, only two channel elements are shown.) The channelelement 210 a demodulates and decodes the baseband signal, and providesthe decoded data, containing the request command to the controller 110.

The decoded data at the controller 110 are forwarded to a call controlprocessor (CCP) 212. The call control processor 212 selects one ofselector elements (SE) 214, and sends to the selected selector element214 a a command to direct base station 104 c to assign a forward linktraffic channel. (For simplicity, only one selector element is shown.)Base station 104 c uses the channel element 210 a to control the callwith subscriber station 106 a. After the forward traffic channel hasbeen assigned, call control processor 212 is informed. The call controlprocessor 212 then commands base station 104 c to transmit a channelassignment message to subscriber station 106 a on the forward link 204,and to configure the selector element 214 to interface the forthcomingvoice call to the PSTN 112.

The subscriber station 106 a receives the forward link signal 204 on anantenna 224 and routes the forward link signal 204 to a front end (FE)226. The front end 226 filters, amplifies, downconverts, and quantizesthe received signal and provides a resultant digitized baseband signalto demodulator (DMD) 228. The digitized baseband signal is demodulatedby demodulator 228 and decoded by a decoder (DCD) 230. The decoded data,which contains the channel assignment message, is routed to a controller(SCTR) 232. The controller 232 receives the channel assignment messageand configures the subscriber station 106 a to voice call datatransmission.

The data transmission procedure from the subscriber station 106 startsby a data source (DSM) 238 at the mobile station 106 a indicating thatdata is present for transmission to a controller (MCTR) 232. Thecontroller 232 can be implemented in a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. The controller 232 may contain a memory(external or internal to the controller 232) that can be implementedusing a storage element or one of any number of memory devices, such asRAM memory devices, latches, or other types of memory devices, that areknown in the art. The controller 232 processes the indication by routinga request command to an encoder (ENC) 236. The encoder 236 encodes therequest command and provides the encoded request to a modulator (MOD)234. Modulator 234 modulates the signal with the selected modulationscheme, and provides the modulated signal to the front end 226. Thefront end 226 filters, amplifies, and transmits the signal over the air,through antenna 224, on the reverse link 202.

The base station 104 c receives the request at the antenna 206 andprovides the request to the RF unit 208. The RF unit 208 filters,amplifies, downconverts, and quantizes the reverse link signal andprovides a digitized baseband signal to one of channel elements 210,e.g., 210 a. The channel element 210 a demodulates and decodes thebaseband signal, and provides the decoded data, containing the requestcommand to the controller 110.

The decoded data at the controller 110 is forwarded to a channelscheduler (CSH) 218. The channel scheduler 218, connected to allselector elements 214 within base station controller 110, assigns themaximum scheduled transmission rate that can be used by the subscriberstation 106 c for high speed data transmission on the reverse link inaccordance with a method described below. The maximum scheduledtransmission rates for subscriber station 106 is provided to one of theselector elements 214. Selector element 214 routes the schedulinginformation to one of the channel elements 210, which encodes andmodulates the scheduling information. The modulated signal is providedto the RF unit 208, which upconverts, filters, and amplifies the signal.The signal is transmitted by antenna over forward link 202. The selectorelement 214 is configured to interface the forthcoming data to the DNI114.

At the subscriber station 106 c, the forward link signal is received bythe antenna 60 and processed in the same manner as described with regardto a voice call. The decoded data, which contains the maximum scheduledtransmission rate, is routed to the controller 232. The controller 232receives the scheduling information and configures the hardware to begindata transmission at or below the maximum scheduled transmission rate.

In one embodiment, high speed data transmission occurs in essentiallythe same manner as that described above for transmission of the requestcommand, with the exception that data transmission can occur at rates upto the maximum scheduled transmission rate. At the subscriber station106 c, the data is partitioned into data frames. In this specification,a data frame refers to the amount of data which is transmitted fromsubscriber station 106 to base station 104 within one frame time period.The data frame can be further partitioned into smaller units called dataportions. The data frames are sent from a data source 238 to an encoder236. Encoder 236 formats the data frames. In one embodiment, a methodfor encoding and interleaving the data as described in detail in theaforementioned U.S. Pat. No. 5,504,773 is used. The encoded data framesare provided to a modulator 234, which modulates the data, and providesthe modulated data to the front end 226. The front end 226 filters,amplifies, upconverts and transmits the signal over the air throughantenna 224 on the reverse link 204.

The base station 104 c receives the reverse link signal and demodulatesand decodes the reverse link signal in the manner described above. Thedecoded data is provided by a channel element 210 to a selector element210. Selector element 214 provides the data to packet network interface114, which routes the data to data sink 222.

Considering the description above, the reverse link transmission iscarried out in two modes consistent with the characteristics of voiceand data communication as discussed. In the first mode, thecommunication between base stations 104 and subscriber stations 106 isnot scheduled because of intolerance to additional processing delay.This mode includes voice communications. In the second mode, thecommunication between base stations 104 and subscriber stations 106 isscheduled, and includes data communications, which can tolerateadditional processing and queuing delay.

One of ordinary skill in the art would understand that the previousdescription is meant to describe basic access procedures. Consequently,the access procedures described, as well as functions and blocksperforming the functions, can also be accomplished by otherimplementations. Thus, for example, the locations of channel scheduler218 and selector element 214 depend on whether a centralized ordistributed scheduling processing is desired. For example, channelscheduler 218 and selector element 214 can be included within basestations 104. This distributed processing allows each base station 104to perform its own scheduling, thereby possibly minimizing theprocessing delay. Conversely, channel scheduler 218 can be designed tocontrol communication with all base stations 104 in the communicationsystem. This centralized processing may result in the optimalutilization of system resources. However, centralized scheduling is morecomplex because of the various interactions between the cells andsubscriber stations 106. In an alternative embodiment, specificallyapplicable to CDMA communication systems, to simplify the scheduling,the scheduled tasks can be divided into two categories: scheduled tasksfor subscriber stations 106 which are in soft handoff and scheduledtasks for subscriber stations 106 which are not in soft handoff. In thealternative embodiment, the reverse link rate scheduling for subscriberstations 106, that are in communication with only one cell can beperformed at the cell level. Subscriber stations 106, which are incommunication with multiple cells can be scheduled by a central channelscheduler 218. The present invention incorporates all embodiments of theforward link rate scheduling, including centralized scheduling,distributed scheduling, and any combinations thereof.

In one embodiment, the channel scheduler 218 is tasked with the functionof assigning the data transmission rate to each subscriber station 106within the communication system 100 such that a set of goals isoptimized. These goals include, but are not limited to: (1) improvedutilization of the reverse link capacity by transmitting as manyscheduled and unscheduled tasks as can be supported within systemcapacity constraints, (2) improved quality in the communication andminimized transmission delay, (3) fair allocation of the reverse linkcapacity to all scheduled users based on a set of priorities, and (4)minimized transmit power of subscriber station 106 to extend batterylife and reduce interference. The goals are optimized by balancing alist of factors, which in general depend on an implementation of thecommunication system 100. A discussion of factors pertaining to a CDMAcommunication system is detailed in the aforementioned U.S. Pat. Nos.5,914,950 and 5,923,659.

In certain situations, the scheduler 218 has an advanced knowledge thata subscriber station 106 will have data to be transmitted on the reverselink at an ascertainable time in the future. In accordance with anembodiment, the scheduler utilizes this knowledge to optimize the set ofgoals by scheduling a transmission on the reverse link without a requestfor such a scheduling from the subscriber station 106. The knowledge maybe based on an existence of a feedback relationship. The knowledge mayalso be based on an existence of pre-scheduled transmission from thesubscriber station 106.

An example of the feedback relationship is an Automatic RetransmissionreQuest (ARQ) method, often used at the link layer of communicationsystems to detect missing or erroneously received information at thereceiving terminal, and request retransmission of this information atthe transmitting terminal. An example of such an ARQ is a Radio LinkProtocol (RLP), a class of error control protocols known as negativeacknowledgement-based (NAK) ARQ protocols, which are well known in theart. One such RLP is described in TIA/EIA/IS-707-A.8, entitled “DATASERVICE OPTIONS FOR SPREAD SPECTRUM SYSTEMS: RADIO LINK PROTOCOL TYPE2”, hereinafter referred to as RLP2. The existing link layer ARQ schemesachieve retransmission of missing or erroneously received packets byutilizing a sequence number unique to each packet. When a receivingterminal detects a packet with a sequence number higher than an expectedsequence number, the receiving terminal declares packet(s) with sequencenumber(s) between the expected sequence number and the detected packet'ssequence number missing or erroneously received. The receiving terminalthen sends a control message requesting retransmission of the missingpackets to a transmitting terminal. Alternatively, the transmittingterminal may resend the packet after a certain time out interval if thetransmitting terminal has not received a positive acknowledgement fromthe receiving terminal. Consequently, existing link layer ARQ schemescause a large delay between the first transmission of a packet and asubsequent retransmission. However, regardless of a particular ARQscheme, the scheduler 218 has an advanced knowledge that a subscriberstation 106 will need to transmit a feedback message at a certain timeafter the packet has been sent from the base station 104.

An example of a pre-scheduled transmission from the subscriber station106 is when a sensor or a set of sensors, each connected to acorresponding subscriber station 106, is pre-scheduled to reportaccumulated data at a certain time. Therefore, the scheduler 218 hasadvanced knowledge that a subscriber station 106 will need to transmitthe accumulated data at the pre-scheduled time.

FIG. 3. illustrates a conceptual block diagram of channel scheduler 218in accordance with an embodiment. A controller (CTR) 302 collectspertinent information, e.g., capacity and queue, from the basestation(s) 104 in the communication system from FIG. 1, and stores thecollected information in a memory element (ME) 304. The collectedinformation may be retrieved by the controller 302 as needed. Thecontroller 302 can be implemented in a general purpose processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. Memory element 304 can be implemented usinga storage element or one of any number of memory devices, such as RAMmemory devices, latches, or other types of memory devices, that areknown in the art. The controller 302 connects to all selector elements214 within the base station controller 110. The controller 302 is alsocoupled to timing element (TE) 306. Timing element 306 can beimplemented with a counter run by a system clock, an on-board oscillatorlocked to an external signal, or a storage element for receiving systemtiming from an external source. Timing element 306 provides controller302 with timing signals necessary to perform the reverse link ratescheduling. The timing signals also allow controller 302 to send thescheduling information to selector element 214 at the appropriateinterval.

FIG. 4 illustrates a flow diagram of a reverse link rate schedulingmethod in accordance with one embodiment. The method starts in step 402.

In step 404, a scheduler determines which subscriber stations will haveto be considered in the current scheduling period. Such subscriberstations comprise the subscriber stations that requested to be scheduledfor a transmission on the reverse link by sending a request command.Such subscriber stations also comprise the subscriber stations that willbe due for a transmission on the reverse link due to the occurrence of acertain event as discussed above. Because the scheduler is provided withtime instances for the pre-scheduled transmission from the subscriberstation, the current time, and the system parameter that determines howlong before transmission a subscriber station sends the request command,the scheduler can determine when each of the pre-scheduled subscriberstations would send a request command. The scheduler also keeps track ofthe packets that were sent to base stations on the forward link, andcan, therefore, determine based on a transmission delay and errorstatistics, when each of these base stations receives a packet thatrequires acknowledgement. Consequently, the scheduler can determine wheneach of these subscriber stations would send a request command.

In step 406, the scheduler collects all pertinent information necessaryfor the optimal scheduling assignment of the data transmission for eachsubscriber station that was determined in step 404. The pertinentinformation may include the number of scheduled and unscheduled tasks,the transmit power available to each subscriber station, the queue sizeindicating the amount of data to be transmitted by each subscriberstation, the transmission rate for the unscheduled task for eachdetermined subscriber station during the prior scheduling periods, thelisting of base stations with which the subscriber station cancommunicate, the priority of subscriber stations, the total powerreceived at each cell for the prior scheduling period, and otherparameters known to one skilled in the art.

In step 408, the scheduler determines scheduling information for eachscheduled subscriber station based on the collected information and theset of aforementioned goals. The scheduling information is dependent onthe constraints of the communication system. Thus if the communicationsystem supports a variable transmission rate on the reverse channel, thescheduling information may comprise a maximum transmission rate and timeinstance in which each of the scheduled subscriber station may transmit.Examples of such systems are a CDMA system, a GLOBALSTAR system, a timedivision multiple access (TDMA) system, or a frequency division multipleaccess (FDMA) system. The application of the present invention to a CDMAsystem or other variable rate communication systems, using the conceptof a single variable rate channel, or multiple channels having a fixedrate, or a combination of variable and fixed rate channels, is withinthe scope of the present invention.

In one embodiment of the invention, certain subscriber stations do notneed to send a request to transmit. The permission to transmit isimplied from an occurrence of an event, a receipt of a packet requiringan acknowledgement, or incidence of a pre-scheduled time to transmit. Inthis embodiment, the scheduling information is pre-determined. Thus, forexample, a subscriber station that received a packet requiring anacknowledgement will transmit acknowledgement data at a pre-determinedtransmission rate and a pre-determined time instance after receiving thepacket. The scheduler may always modify the pre-determined schedulinginformation by transmitting new scheduling information.

In another embodiment of the invention, all subscriber stations arerequired to send a request command. The scheduler may transmit tocertain subscriber stations scheduling information that contains apermission to transmit without the need for a request command.

In either embodiment, the scheduler may transmit a command requiring asubscriber station that was not required to send a request command to doso and vice versa.

Consequently, in step 410, the scheduler transmits the schedulinginformation to the subscriber station.

The reverse link rate scheduling in accordance with the followingembodiments can be performed continuously, periodically, or in astaggered manner. If the scheduling is performed continuously orperiodically, the scheduling interval is selected such that the reverselink capacity of the cells is fully utilized for the duration of thescheduling period. In accordance with the embodiments, the minimumperiod is a code data frame. As discussed, data to be sent ispartitioned into data packets. The data packets are then encoded intocode channel frames, and the code frames are transmitted.

In the first embodiment, the scheduling is performed every frame. Thisembodiment allows the channel scheduler to dynamically adjust themaximum scheduled transmission rate of the scheduled user at each frameto fully utilize the capacity available for each cell in the network.More processing is required to assign the scheduled information at eachframe. Also, the scheduler collects all pertinent information morefrequently.

In the second embodiment, the scheduling is performed every K frames,where K is an integer greater than one. On the reverse link, ascheduling delay exists from the time the data is made available to thesubscriber station to the time of data transmission at the high speedtransmission rate. In the exemplary embodiment, the scheduling delay canbe up to several frames in length. The scheduling delay impacts theresponsiveness of the channel scheduler to changes in the reverse linkcapacity and demand. When the reverse link is lightly loaded, allowingthe subscriber station to transmit at any rate up to the maximumscheduled transmission rate, the scheduling delay is reduced. When asubscriber station has no more data to transmit, the subscriber stationcan immediately reduce the transmission rate and, thus, reduce thereverse link interference to other subscriber stations. Additionally,less overhead is required to transmit the scheduling information to thesubscriber stations. Because a portion of the forward link resource isallocated to overhead, reducing transmission of the overhead isachieved. For example, if the scheduling interval is ten frames, thesecond embodiment requires slightly more than 1/10 of the overhead ofthe first embodiment while still maintaining efficient utilization ofthe reverse link.

Alternately, in the third embodiment, the reverse link rate schedulingcan be staggered. In this embodiment, the scheduling is triggered bycertain events. For example, the channel scheduler can perform thereverse link rate scheduling whenever a request for high speed datatransmission is received or whenever a scheduled high speed datatransmission by the subscriber station is completed. The channelscheduler has knowledge of the amount of data to be transmitted by eachsubscriber station and the scheduled transmission rate. Thus, thechannel scheduler is able to determine when the high speed datatransmission is completed. Upon termination of a scheduled transmissionby the subscriber station, the channel scheduler can perform thescheduling and allocate the reverse link capacity to other subscriberstations.

One skilled in the art recognizes that the embodiments can be combined,i.e., certain subscriber stations can be scheduled periodically on aframe or K-frame period, and other subscriber stations can be scheduledupon an event occurrence. For example, the channel scheduler hasknowledge of the data packets to be transmitted to each subscriberstation and the scheduled transmission rate. Consequently, the channelscheduler is able to determine when a particular subscriber stationrequests acknowledgement transmission, schedule the acknowledgementtransmission, and transmit schedule information to the particularsubscriber station. As discussed, this results in better resourceutilization because the particular subscriber station does not need torequest scheduling information. Furthermore, because the scheduler hasaccess to the data packets, it can add the scheduling information to thedata packet(s), and transmit the data packet(s) and the schedulinginformation together, thus achieving further resource savings.

Consequently, in step 412, the scheduler determines whether the nextscheduling period has started. If the determination is negative, themethod returns to step 412. Otherwise, the method returns to step 404 torestart the scheduling cycle.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

1. A method for scheduling transmission on a link in a communicationsystem, comprising: transmitting data on a first link in thecommunication system; determining a transmission schedule to transmitdata based on a forthcoming event for at least one subscriber stationdue for a transmission of the data, before the subscriber station sendsa request for transmission; and transmitting scheduling information onthe first link in the communication system.
 2. The method as claimed inclaim 1, wherein said transmitting scheduling information on the firstlink in the communication system comprises: transmitting schedulinginformation together with said transmitted data on the first link in thecommunication system.
 3. A method for scheduling transmission on a linkin a communication system, comprising: transmitting data on a first linkin the communication system; determining a transmission schedule totransmit data based on a forthcoming event for at least one subscriberstation due for a transmission of the data, before the subscriberstation sends a request for transmission; and scheduling transmission onthe link in the communication system in accordance with a reception ofsaid transmitted data on the first link.
 4. The method as claimed inclaim 3, wherein said scheduling transmission on the link in thecommunication system in accordance with a reception of said transmitteddata on the first link comprises: scheduling transmission on the link inthe communication system at a first time instance delayed by apre-determined amount from a time instance of the reception of saidtransmitted data on the first link.
 5. The method as claimed in claim 3,further comprising: ascertaining the link capacity at a base stationexpecting said scheduled transmission on the link in the communicationsystem in accordance with the reception of said transmitted data on thefirst link; and transmitting, on the first link in the communicationsystem, a change to at least one parameter of said scheduledtransmission when said ascertained link capacity does not support saidscheduled transmission.
 6. The method as claimed in claim 5, whereinsaid transmitting, on the first link in the communication system, achange to at least one parameter of said scheduled transmission whensaid ascertained link capacity does not support said scheduledtransmission comprises: transmitting, on the first link in thecommunication system, a change to at least one parameter of saidscheduled transmission together with said transmitted data.
 7. A methodfor scheduling transmission on a link in a communication system,comprising: ascertaining the link capacity at a base station expecting apre-scheduled transmission of data on the link wherein a transmissionschedule to transmit the data is based on a forthcoming event of atleast one subscriber station due for a transmission of the data, beforethe subscriber station sends a request for transmission; and proceedingin accordance with said ascertained link capacity.
 8. The method asclaimed in claim 7, wherein said proceeding comprises: abstaining fromtransmitting scheduling information on a first link when saidascertained link capacity supports the pre-scheduled transmission ofdata.
 9. The method as claimed in claim 8, further comprising:transmitting re-scheduling information on a first link when saidascertained link capacity does not support the pre-scheduledtransmission of data.
 10. The method as claimed in claim 7, wherein saidproceeding comprises: transmitting, on the first link, authorization forthe pre-scheduled transmission of data when said ascertained linkcapacity supports the pre-scheduled transmission of data.
 11. The methodas claimed in claim 10, further comprising: transmitting re-schedulinginformation on the first link when said ascertained link capacity doesnot support the pre-scheduled transmission of data.
 12. An apparatus forscheduling transmission on a link in a communication system, comprising:a transmitter; a processor; and a storage medium coupled to theprocessor and containing a set of instructions executable by theprocessor to cause the transmitter to transmit data on a first link inthe communication system, determine a transmission schedule to transmitdata based on a forthcoming event for at least one subscriber stationdue for a transmission of the data, before the subscriber station sendsa request for transmission, and cause the transmitter to transmitscheduling information on the first link in the communication system.13. The apparatus as claimed in claim 12, wherein the set ofinstructions executable by the processor to cause the transmitter totransmit data on a first link in the communication system comprises aset of instructions executable by the processor to cause the transmitterto transmit the scheduling information together with the transmitteddata on the first link in the communication system.
 14. An apparatus forscheduling transmission on a link in a communication system, comprising:a transmitter configured to transmit data on a first link in thecommunication system; a processor; and a storage medium coupled to theprocessor and containing a set of instructions executable by theprocessor to determine a transmission schedule to transmit data based ona forthcoming event for at least one subscriber station due for atransmission of the data, before the subscriber station sends a requestfor transmission, and to schedule transmission on the link in thecommunication system in accordance with a reception of the transmitteddata on a first link.
 15. The apparatus as claimed in claim 14, whereinthe set of instructions executable by the processor to scheduletransmission on the link in the communication system in accordance witha reception of the transmitted data on a first link comprises a set ofinstructions executable by the processor to schedule transmission on thelink in the communication system at a time instance delayed by apre-determined amount from a time instance of the reception of thetransmitted data on the first link.
 16. The apparatus as claimed inclaim 14, further comprising: a second processor; and a second storagemedium coupled to the second processor and containing a set ofinstructions executable by the second processor to ascertain the linkcapacity at a base station expecting the scheduled transmission on thelink in the communication system in accordance with the reception of thetransmitted data on the first link; and cause the transmitter totransmit, on the first link in the communication system, a change to atleast one parameter of the scheduled transmission when the ascertainedlink capacity does not support the scheduled transmission.
 17. Theapparatus as claimed in claim 16, wherein the set of instructionsexecutable by the second processor to cause the transmitter to transmit,on the first link in the communication system, a change to at least oneparameter of the scheduled transmission when the ascertained linkcapacity does not support the scheduled transmission comprises a set ofinstructions to cause the transmitter to transmit, on the first link inthe communication system, a change to at least one parameter of thescheduled transmission together with the transmitted data.
 18. Anapparatus for scheduling transmission on a link in a communicationsystem, comprising: a processor; a storage medium coupled to theprocessor and containing a set of instructions executable by theprocessor to ascertain the link capacity at a base station expectingtransmission of a pre-scheduled data on the link wherein a transmissionschedule to transmit the data based on a forthcoming event of at leastone subscriber station due for a transmission of the data, before thesubscriber station sends a request for transmission, and proceed inaccordance with the ascertained link capacity.
 19. The apparatus asclaimed in claim 18, further comprising a transmitter, wherein the setof instructions executable by the processor to proceed in accordancewith the ascertained link capacity comprises a set of instructionsexecutable by the processor to abstain from transmitting schedulinginformation on a first link when the ascertained link capacity supportsthe pre-scheduled transmission of data.
 20. The apparatus as claimed inclaim 19, wherein the set of instructions further comprises a set ofinstructions executable by the processor to cause the transmitter totransmit re-scheduling information on the first link when theascertained link capacity does not support the pre-scheduledtransmission of data.
 21. The apparatus as claimed in claim 18, furthercomprising a transmitter, wherein the set of instructions executable bythe processor to proceed in accordance with the ascertained linkcapacity comprises a set of instructions executable by the processor tocause the transmitter to transmit authorization for the pre-scheduledtransmission of data on a first link when the ascertained link capacitysupports pre-scheduled transmission of data.
 22. The apparatus asclaimed in claim 21, wherein the set of instructions further comprises aset of instructions executable by the processor to cause the transmitterto transmit re-scheduling information on the first link when theascertained link capacity does not support the pre-scheduledtransmission of data.
 23. A apparatus for scheduling transmission on alink in a communication system, comprising: means for ascertaining thelink capacity at a base station expecting a pre-scheduled transmissionof data on the link wherein a transmission schedule to transmit the datais based on a forthcoming event of at least one subscriber station duefor a transmission of the data, before the subscriber station sends arequest for transmission; and means for proceeding in accordance withsaid ascertained link capacity.
 24. The apparatus as claimed in claim23, further comprising: means for abstaining from transmittingscheduling information on a first link when said ascertained linkcapacity supports the pre-scheduled transmission of data.
 25. Theapparatus as claimed in claim 24 further comprising: means fortransmitting re-scheduling information on a first link when saidascertained link capacity does not support the pre-scheduledtransmission of data.
 26. The apparatus as claimed in claim 23, whereinsaid proceeding comprises: means for transmitting, on the first link,authorization for the pre-scheduled transmission of data when saidascertained link capacity supports the pre-scheduled transmission ofdata.
 27. The apparatus as claimed in claim 26 further comprising: meansfor transmitting re-scheduling information on the first link when saidascertained link capacity does not support the pre-scheduledtransmission of data.